Growling front end noise!

[Mark Graham]

Hello,

My 86 Quattro is making a growling noise in the front end. Mostly when 
turning left, or holding slight pressure on the steering to the left. I have 
jacked the car up and checked wheel bearing, and they seem to be tight. I 
have replaced the left axle & CV joints two years ago, but not the right.

Further inspection, I have found the gear housing carrier rear seal has been 
leaking (but not leaving any spots when parked) and wondering if it has 
pumped all of its oil out on the road? What "mm" size is the gear filler plug 
so I can purchase a wrench to check the oil level? And if it has pumped all 
of its oil out, would this be the noise source, and should I be looking for 
another gearbox/differential?

Advice and guidance would be greatly appreciated!